1. Industrial Field of the Invention
The present invention relates to a color sensor for use in inspecting and controlling colors of such products as color prints, products coated with color paint, plastic products, foods, chemicals and so on including raw materials for the above of them being conveyed on the production line.
2. Prior Art
In FIG. 4, there is shown a known arrangement including a color sensor, which comprises a light source 1 for emitting illuminating light, light guides 2, a probe 3, a light receiving device 4, an amplifier 5 and an object 6 being examined, and an arrow 7 indicating extraneous disturbing light.
The color sensor thus constituted is disadvantageous in that, when the intensity/color of the illuminating light changes or when extraneous light is incident on the object being examined, the output value of the light receiving device 4 differs from the measured one that ought to be indicated.
In order to remedy this drawback, the extraneous light should be shut out while a light source for emitting illuminating light free from a change in intensity/color is used. However, it is almost impossible to provide such a light source for emitting illuminating light completely free from variations in intensity/color.
A color sensor shown in FIG. 5 has been proposed to solve the aforesaid problem. As shown in FIG. 5, this color sensor comprises light receiving devices 4a, 4b, a comparing operational device 8 and other parts with reference characters given to corresponding or like parts of FIG. 4. In the case of the color sensor thus constituted, the output value can be corrected, even though its illuminating light changes, by correcting the output value of one light receiving device 4b receiving the light reflected from an object 6 being examined while making use of the output value of the other light receiving device 4a for directly receiving the illuminating light from the light source.
Notwithstanding, the color sensor of FIG. 5 is still vulnerable to extraneous light as in the case of what is shown in FIG. 4 however sophisticatedly it may be contrived. In other words, the color of the object will have to be examined while the extranous light is shut out by, for istance, taking out the object being examined from the conveyor belt and putting it into a darkbox or arranging the conveyor belt in a darkroom.
However, any one of the aforesaid techniques will make the production line inconvenient for use, thus decreasing productivity.
Another known arrangement is to create the same condition as that in the darkroom by having a probe directly contact an object being examined. In this case, it incurs the risk of bruising the object being examined.